Identification of microtubule proteins in griseofulvin sensitive and resistant yeasts.

The effects of the anti-fungal antibiotic griseofulvin on the growth and cytology of a sensitive yeast Protomyces inundatus were investigated using light, scanning and transmission electron microscopic techniques. This drug was found to inhibit the growth of Protomyces, causing the cells to be arrested in cell division. Electron microscopy revealed that griseofulvin did not cause the disaggregation of nuclear microtubules, however the microtubules appeared to be assembled in a disorganised manner. Differences in sensitivity to griseofulvin between the insensitive Saccharomyces cerevisiae and Protomyces inundatus were found not to be the result of differences in permeability to the drug. Both yeasts appeared to take up the drug very rapidly and to a similar extent. The problems associated with the study of griseofulvin uptake are highlighted and discussed.

Microtubule proteins were investigated in Saccharomyces cerevisiae. Initial attempts to purify microtubules from this yeast by assembly-disassembly were unsuccessful due to the inhibitory activity present in the Saccharomyces extracts. Protease activity, GTP-ase activity and RNA were found to contribute to this inhibitory activity. The addition of glycerol to assembly mixtures also reduced the inhibition. Microtubule proteins were identified from Saccharomyces cerevisiae by co-polymerisation of 3%-labelled cell extract with brain microtubule protein which was either unmodified or depleted in microtubule-associated proteins (MAPs) by assembly in dimethyl sulphoxide (DMSO). Using this technique, a number of radioactive proteins co-polymerising throughout three cycles of assembly-disassembly were detected.. These had estimated SDS-molecular weights of 230,000; 200,000; 130,000; 110,000; 73,000; 55,000; 52,000 and 49,000 daltons. The 55,000 and 52,000 dalton proteins eluted in the unbound fraction i.e. behaved as tubulin, during phosphocellulose chromatography of the copolymer. The 55,000 dalton protein co-migrated with brain β-tubulin on sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), however no yeast protein co-migrating with brain tubulin was observed. Remaining co-polymerised Saccharomyces proteins bound to phosphocellulose and were eluted with 0.25-0.5M salt. Saccharomyces co-polymer preparations assembled with a reduced critical concentration compared with a control, and contained ring-like structures in depolymerised preparations, which were absent in the control suggesting the presence of yeast MAPs. Similar co-polymerisation was performed using Protomyces inundatus. Differences in putative MAPs were observed compared with Saccharomyces cerevisiae.